Woop, a HACKING document for openbox at last!

Beware the Client.transient_for. It can be set to a !NULL value of TRAN_GROUP,
which is not a valid pointer. You must ALWAYS check for TRAN_GROUP before
following transient_for. When TRAN_GROUP is found, Client.group will always
be !NULL. Some smart action should be taken using all members of the group in
this case.

When using coordinates/sizes of windows, make sure you use the right area. The
Client.area rect is the reference point and size of the *CLIENT* window. This
value is not what you see in any shape or form, and gravity is applied to it to
translate it into what you see. The Client.frame.area is the actual position
and size of the entire frame. This is usually the value you want to use, unless
you are in client.c (probably) and adjusting/using the position or size from
the client's perspective.